1. Field of the Invention
The present invention relates generally to a wireless digital broadcasting system, and more particularly, to a method and apparatus for transmitting and receiving in-band signaling information.
2. Description of the Related Art
In an information society of the 21st century, broadcast communication services have begun to enter an era of digitalization, multi-channelization, broadband, high-quality, etc. Particularly, the recent increasing popularization of portable broadcast devices, including high-definition digital televisions and Portable Multimedia Players (PMP), has increased demands for supporting various reception methods of digital broadcast services.
FIG. 1 illustrates a transmission scheme in a conventional broadcasting system.
Referring to FIG. 1, reference numeral 101 indicates one frame. Commonly, the frame 101 includes a preamble 102, a P2-L1 signaling 103, a PLP0-L2 signaling 104, and one or more Physical Layer Pipes (PLPs) 105, 106 and 107. The preamble 102 is a signal generally used to acquire time and frequency synchronization, and synchronization for a frame boundary at a receiver. P2-L1 signaling 103 is a part of the frame 101 where an L1 signaling is transmitted. The L1 signaling, as illustrated in FIG. 1, is also referred to as P2, and means a Layer 1 signaling, or physical layer signaling.
The P2-L1 signaling 103, or the physical layer signaling, includes L1 static information 108, L1 configurable information 109, and L1 dynamic information 110. The L1 static information 108 includes information that is basically static over the passage of time, and such static information may include information on a cell identifier, a network identifier, the number of Radio Frequency (RF) channels, a frame length, a pilot subcarrier location, etc.
The L1 configurable information 109 includes information that may change once in a while, without changing on a frame-by-frame basis, i.e., information that generally lasts for a plurality of frames. Such configurable information may include information on a service identifier, a modulation order used for data transmission for an individual service, a code rate, etc. The L1 dynamic information 110 includes information that may change on a frame-by-frame basis. Such dynamic information may include information about a location where each PLP is transmitted in the current frame, i.e. information about where each PLP starts and ends in the current frame.
The PLP0-L2 signaling 104 is a part of the frame 101 through which an L2 signaling is transmitted. The L2 signaling represents a Layer 2 signaling, or a Medium Access Control (MAC) signaling. Generally, a PLP over which the L2 information is transmitted is also referred to as a PLP0. The PLP0 includes connection information between PLPs and broadcast services to indicate PLPs through which particular services are received. In FIG. 1, the PLP_1 105, the PLP_2 106 and the PLP_N 107 each transmit one or a plurality of broadcast service channels, and are parts of the frame 101 through which actual broadcast data is transmitted, so they can also be referred to as “data PLPs.” The data PLPs are PLPs transmitted by Time Division Multiplexing (TDM). The data PLP will be referred to herein as a “data PLP for a broadcast service.”
A process of actually receiving a particular broadcast service channel is described with reference to FIG. 1. After acquiring synchronization of the frame through the preamble 102, a receiver gets such information as a transmission scheme by which data is transmitted and a frame length using the P2 part 103, acquires, from the PLP0 104, information indicating a PLP(s) through which its desired a broadcast service channel is transmitted, and then receives broadcast data through the data PLPs 105, 106 and 107.
In order to allow the receiver bypass the above-described process of receiving the preamble, the P2, the PLP0 and the data PLPs in sequence every frame when it receives a particular broadcast service for a predetermined time, a technology is used that transmits same PLP's L1 dynamic information in a next frame, on a PLP for the particular broadcast service using in-band signaling. A data reception method based on in-band signaling is illustrated in FIG. 2A.
FIG. 2A illustrates an example of a data reception method in a basic in-band signaling system.
Referring to FIG. 2A, a frame #k 201 and a frame #(k+1) 20 are shown. Frame #k includes a preamble 203, P2-L1 signaling 204, PLP0-L2 signaling 205, PLP_1 206, PLP_2 207 and PLP_N 208, as described in connection with FIG. 1. Frame #(k+1) 202 includes a preamble 209, P2-L1 signaling 210, PLP0-L2 signaling 211, PLP_1 212, PLP_2 213 and PLP_N 214.
Assume that a particular receiver is receiving a particular broadcast service channel through a PLP_2, as illustrated in FIG. 2A. The receiver receives the PLP_2 207 being transmitted in the frame #k 201. The PLP_2 207 includes in-band signaling information. The in-band signaling information may include a location, or dynamic information, of the PLP_2 207 in the next frame, i.e. the frame #(k+1) 202. Based on the dynamic information, the receiver can directly receive the PLP_2 213 in the next frame, without receiving the P2 part 210 to receive the PLP_2 213 as indicated by reference numeral 217. That is, after receiving the PLP_2 207 in the frame #k 201, the receiver may power off its receiving units until it receives the PLP_2 213 (including the next data) of the frame #(k+1) 202, i.e. the next frame, thereby saving the power.
The PLP_2 207 in the frame #k 201 and the PLP_2 213 in the frame #(k+1) 202 have data for the same broadcast service. In order to distinguish the PLPs, the PLP_2 213 transmitted after the PLP_2 207 in the frame #k, which the receiver is presently receiving, can also be referred to herein as a “next packet.” However, the term “next packet” may indicate a data PLP included in any of frames, including not only the frame right after the current frame, but also all its succeeding frames.
The in-band signaling information 216 may include location(s) of one or multiple different data PLPs as indicated by reference numeral 218. When the receiver makes service switching to the PLP_N 214 while receiving the PLP_2 207, the receiver can obtain location information of the PLP_N 214 in the next frame in advance using the already acquired in-band signaling information. Therefore, the receiver can immediately determine the location of the PLP_N 214 without receiving and demodulating the P2 part 210 of the next frame, thereby reducing its power consumption.
It is assumed in the basic system of FIG. 2A that the in-band signaling information always includes the location and control information of the immediately next frame (frame #(k+1)) after the current frame (frame #k). However, in case that the PLP_2 207 does not exist in the next frame, an extended system can be defined.
FIG. 2B illustrates an example of a data reception method in an extended in-band signaling system. Frame #k 251 includes a preamble 253, P2-L1 signaling 254, PLP0-L2 signaling 255, PLP_1 256, PLP_2 257 and PLP_N 258. Frame #(k+N) 252 includes a preamble 259, P2-L1 signaling 260, PLP0 signaling 261, PLP_1 262, PLP_2 263 and PLP_N 264.
In FIG. 2B, when PLP_2 257 exists in the current frame #k 251 and the next packet exists not in the next frame #(k+1), but in frame #(k+N) 252 (where N is a natural number greater than or equal to 2), it is possible to record location information of the frame #(k+N) 252 in in-band signaling information as shown by reference numeral 270 in FIG. 2B. This scenario is available when a transmitter can store data PLPs for all services in advance, and a definition thereof can be given only when it is possible to predict location information of data PLPs for all the services in advance, for multiple frames. However, the extended system is unavailable when it is not possible to collect all data PLPs with regard to multiple succeeding frames.
The transmitter in the basic system can schedule up to the next one frame immediately after the current frame, while the transmitter in the extended system can schedule up to the next NMAX frames after the current frame (when the current frame is a frame #k, the last one of the next NMAX frames becomes a frame #(k+NMAX)). A combined system is referred to as a broadcasting system herein, and the maximum number of frames (the maximum number of predictable frames) that the transmitter can schedule is defined as the maximum schedulable period NMAX (where NMAX is a natural number greater than or equal to 1). However, in the broadcasting system, when the next packet after a data PLP for a particular broadcast service exists in a frame #(NMAX+1), i.e. when the next packet after a particular data PLP exists in a frame after the last one of the next NMAX frames that the transmitter can schedule, information to be included in in-band signaling information becomes uncertain, making seamless reception impossible at a receiver operating in in-band signaling. Therefore, when an index of the frame where the next packet is transmitted exceeds the maximum number of frames that the transmitter can schedule, receivers cannot receive the packet, causing a packet loss. When an attempt to prevent the packet loss is made, the receivers cannot acquire scheduling information for the next packet until it receives and demodulates L1 signaling from a preamble P2 after a delay of the frame #(NMAX+1) which is the next frame, generating a fatal error.